Synthesis, structure, and photoluminescence of a (4,6)-connected Cu(I)–CN–triazolate framework built with a unique heptanuclear hybrid cluster

Abstract

A 3-D Cu(I)–CN–triazolate hybrid coordination polymer, {Cu₉(NH₂-BPT)₂(BPT)₂(CN)₇}_n (1) (NH₂-BPT = 4-amino-3,5-bis(3-pyridyl)-1,2,4-triazole, BPT = 3,5-bis(3-pyridyl)-1,2,4-triazole), has been synthesized via self-assembly of NH₂-BPT, CuCN, and K₃Fe(CN)₆ under hydrothermal conditions. Single-crystal X-ray diffraction data show that four of the five independent copper centers in 1 have a three-coordinated trigonal coordination geometry, and the remaining copper center has a two-coordinated linear geometry. Three Cu ions are linked by one cisoid-BPT and two CN⁻ to form a 16-membered ring subunit, which is joined by the two-coordinate copper center via the triazole N(4)-position to generate an unprecedented [Cu₇(BPT)₂(CN)₄] hybrid heptanuclear cluster. Each heptanuclear motif is linked to two adjacent [Cu₇] clusters through four CN⁻ anions, and further to four [Cu–CN–Cu] binuclear clusters through two transoid-NH₂-BPT ligands. Each of these [Cu–CN–Cu] units is linked to four neighboring heptanuclear motifs. The overall geometry is a 3-D (4,6)-connected topological framework with Schläfli symbol of (4⁴× 6²)(4⁴× 6¹⁰× 8). Compound 1 also exhibits high thermal stability and strong green fluorescence emission at 536 nm in the solid state.

Keywords:

• Copper cyanide
• 4-amino-3,5-bis(3-pyridyl)-1,2,4-triazole
• Heptanuclear cluster
• Coordination polymer
• Photoluminescence